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RE: Marine question



>>Here all the opthalmosaurids, along with cryptocleidid plesiosaurs
simultaneously disappear. >>

The Cryptoclidids(whatever that means) did not disappear at the J/C
boundary - Kaiwhhekea (CRUICKHSHANK & FORDYCE 2002), from the upper
Haumurian (Cenomanian/Maastrichtian) of New Zealand shows that they survived
pretty well right up to the KT boundary. Ichthyosaur remains are fairly
common in the lower Chalk (Cenomanian); the lack of publication on such
material is largely due to its fragmentary nature rather than a scarcity.

>>..BTW, all K ichthyosaurs are referred to *Platypterygius*.>>
just as all large Cretaceous pliosaurs are referred to *Polyptychondon*.
They ain't: on the basis of tooth morphology (which I know can be unreliable
(and bearing in mind that the holotypes of the first two described species
of *Polyptychondon* are a single isolated tooth))I suspect that at least
three taxa are present in the Cambridge Greensand alone. Scarcity of, or
fragementary material leads to garbage bin taxa.

In my occasional visits to collections to root through the dusty boxes in
the basement I frequently find mis-identified material. After all, if the
book says that there are no ichthyosaurs in the Cretaceous, that bone you're
trying to identify can't be that of an ichthyosaur. So it gets labelled
'plesiosaur', or 'retilia indet' and is never looked at again. I suspect
that if a serious search of collections for late Cretaceous ichthyosaur
material were made, we'd find it rather more common that we suppose.

Richard Forrest
richard@plesiosaur.com
www.plesiosaur.com

"Minds are like parachutes: they only function when they are open"
James Dewar